Question

with others? Oil and water don't mix Gasoline and water also do not mix. However, gasoline and oil do mix. To understand solubility we must look at two important characteristics: geometry and bond polarity (ionic. nonpolar and polar). From these two characteristics the overall molecular polarity can be determined. The statement "like dissolves like" provides a good basis for understanding solubility. A substance with similar characteristics will mix with another substance with similar characteristics. This can be summarized as polar and ionic compounds mix with other polar and lonie compounds. Nonpolar compounds mix only with other nonpolar compounds. To determine overall molecular polarity follow the procedure below: 1. Identify the central atom. The central atom is the least electronegative element. Hydrogen is not a central atom. 2. Place all other atoms around the central atom. 3. Calculate the total number of valence electrons. Include the charge in the electron count. A negative charge results in the addition of electrons while a positive charge results in a subtraction of electrons. 4. Electrons are always placed in pairs to form either bonds represented by a line or lone pairs represented by two dots. Complete the octet for each element (except hydrogen, it only requires 2 electrons) with the valence electrons. Sometimes this takes some trial and error so be sure to use a pencil. If there are not enough electrons then include double or even triple bonds to complete octets. Oxygen frequently forms double bonds and nitrogen frequently forms triple bonds. It should be noted that lone pair electrons only count for the atom with which they are associated. Bonding electrons count for both elements they are bonding 5. Count the number of bonding pairs around the central atom and the number of lone pairs around the central atom. Due to the close proximity of the electrons in double and triple bonds, these count as only one bonding pair for geometry. The geometry of the molecule will be based on what is called VSEPR theory. Valence shell electron pair repulsion theory is the concept that electrons pairs attempt to maximize distance from other electron pairs. This results in predictable geometry. We can predict this geometry using the following table: Bonding Pairs 1-3 Lone Pairs 0-3 1 or 2 Geometry Linear Bent Trigonal planar Trigonal pyramidal Tetrahedral 1 0 4

Answer 1

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